For
the first time ever, a scientist has measured the strength of the
magnetic
field inside Earth's core, some 1,800 miles (2,896 kilometers)
underground.

It
turns out the magnetic field in Earth's
core
is about 50 times
stronger than on the planet's surface, and the new number may help
scientists
narrow down the possible heat sources that fuel the mysterious
processes of the
planet's interior.

"A
measurement of the magnetic field tells us what the energy requirements
are and
what the sources of heat are," said Bruce A. Buffett, a professor of
Earth
and planetary science at the University of California, Berkeley, who
made the
measurement.

Scientists
think that Earth's heat comes from three sources: the residual heat
from the
formation of the planet around 4.5 billion years ago, when the planet
was hot
and molten; the release of gravitational energy as heavy elements sink
to the
bottom of the liquid core; and the radioactive decay of long-lived
elements
such as potassium, uranium and thorium.

The
cooling Earth originally captured its magnetic field from the planetary
disk in
which the solar
system
formed.
That field would
have disappeared within 10,000 years if not for the planet's internal
dynamo,
which regenerates the field thanks to heat produced inside the planet.

The
heat makes the liquid outer core ? which is about 1,400 miles (2,253
km) thick
? boil, or convect, and as the conducting metals rise and then sink
through the
existing magnetic field, they create electrical currents that maintain
the
magnetic field. This roiling dynamo produces a slowly shifting magnetic
field
at the surface.

Buffet
pulled off the geophysics milestone by harnessing the aid of some
distant
helpers: the moon and quasars
? extremely bright
and distant active galaxies.

Quasars
hurl from their luminous hearts a steady stream of radio waves that
provide a consistent
backdrop against which Earth's most minute wigglings are noticeable,
and
measurements of these radio waves from ground-based and satellite
telescopes
allow for very precise data on changes in Earth's rotation axis.

By
looking at these changes, and how they are affected by the moon's
gravitational
tug on the Earth, Buffet was able to make his calculations.

"I
still find it remarkable that we can look to distant quasars to get
insights
into the deep interior of our planet," Buffett said.